Electrostatic discharge (ESD) is a natural phenomenon occurring frequently in daily life. ESD can generate a large current in a short period of time. When the large current generated by the ESD passes through an integrated circuit in a short period of time, it may result in a power consumption much higher than what the integrated circuit can bear, causing physical damage to the integrated circuit and, possibly, circuit failure. In fact, ESD has become a major factor that causes failure of integrated circuits during their manufacture and use.
One approach to reduce or avoid damage caused by ESD is to use an ESD protection device or circuit to protect the integrated circuit. A silicon-controlled rectifier (SCR) is one of the devices suitable for use in ESD protection purpose, because of its high current capability and small layout area. However, a conventional SCR has several disadvantages, such as high trigger voltage (Vtr, the voltage above which the SCR is turned on), low holding voltage (Vh, the voltage below which the SCR is turned off), and slow turn-on speed.